'71 with an LBZ duramax. Need advice on fuel tank.

[01chevduramax]

Hey guys I asked this question in the general forum. Didn't get much action.
I've got the duramax swap pretty close. I'm working on the fuel system. I have a plan, but I'm wanting to hear some feedback on it.

I want to keep the stock tank, and filler. I will tig a 1" bung into the bottom passenger side of the stock tank. Stainless elbow, to brass ball valve. Stainless elbow pointing back towards the drivers side. Stainless nipple across the front of the tank. Adapt to -16AN braided hose. Use a bulkhead 90 fitting through the cab floor. Short hose to -16AN tee under the cab.

From that Tee forward reduce to -8AN to fuel filter/lift pump then to the CP3 straight shot no test port.

Other side of that Tee: short -16 hose to bottom of a 15 gallon fuel cell mounted under the passenger side of the bed.

That fuel cell would get a 1/2" vent line out the top that tees into the filler neck vent on the stock tank.

My thoughts here are: the bottom tank would fill up as I pump gas into the top tank. Then the top tank would fill. Maybe a slow fill??

I'd use the stock fuel tanks sender. Probably put a 0-90 ohm sender for the fuel cell. Hook up a switch to watch top or bottom.

Anyone have any input? Concerns? Advice?
My plumber buddy suggested a brass ball valve to help with dissimilar metals. He got pretty scientific with it. I got lost! Help a brother out!!

[01chevduramax]

Just to throw this in... I'm hoping for 10 to 12 miles to the gallon. It's lifted on 38" tires. It's got a compound turbo setup. Injectors, 5" straight pipe😽

Pretty much not what most people think of when they picture Oregonians saving trees/crunching granola/birkenstocks

[Dieselwrencher]

It sounds like it can be done. -16 sounds rather large for sure. Why not just put a tank in the rear under the bed and eliminate all the fittings that will add up to a lot in a quick amount of time? Or, why not use a newer plastic tank and make a fill tube to go from your original hole in the cab, to the new tank's fill hole. It would require some serious fab, but might be a lot less head ache over time from having one tank fill another tank.

[lower50's]

I had a 1986 nissan p/u pre-runner. It had the stock tank 60L and a 80L tank in the bed that would drain into the stock tank below. It had a 3/8" fill line and 3/8" vent. You could use the stock tank like normal non vented cap. Then fill the 80L tank with a vented cap. I would sometimes fill through the upper tank, empty stock tank. By the time I filled the 80L and drove away there was about 40L left in the upper tank. So it did fill the bottom tank at a half descent rate. Good luck

[01chevduramax]

I put some time in today. I got the Bung welded in. Ended up going with a stainless ball valve. Ran my 1" stainless pipe across the fuel tank at floor level. Used an elbow to turn down. Ran through the cab floor with a 1" npt stainless bulkhead. 8" nipple to a 1" tee. Plugged the rear port in the tee for now. Reduced the front port to 1/2npt. Then braided stainless hose (jegs pro flow 200) to the lift pump. Ran 1/2" stainless fuel line with Swagelok fittings up to the engine. Waiting for parts to finish the return lines.

I guess I'll drive it like that for now. Ill build the second tank with aluminum. Doing the math it should be 15-20 gallons or so. I'm hoping for 16mpg with it. (38" tires).
id be looking at almost 600 miles for range!